Geers, M.G.D.

Hoefnagels, J.P.M.

Neggers, J.

English

Neggers, J Jan

Hoefnagels, JPM Johan

Geers, MGD Marc

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A novel route towards interface integrity in stretchable electronics

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 A novel route towards interface integrity in stretchableelectronicsCitation for published version (APA):Neggers, J., Hoefnagels, J. P. M., & Geers, M. G. D. (2010). A novel route towards interface integrity instretchable electronics. Poster session presented at Mate Poster Award 2010 : 15th Annual Poster Contest.Document status and date:Published: 01/01/2010Document Version:Publisher’s PDF, also known as Version of Record (includes final page, issue and volume numbers)Please check the document version of this publication:• A submitted manuscript is the version of the article upon submission and before peer-review. There can beimportant differences between the submitted version and the official published version of record. Peopleinterested in the research are advised to contact the author for the final version of the publication, or visit theDOI to the publisher's website.• The final author version and the galley proof are versions of the publication after peer review.• The final published version features the final layout of the paper including the volume, issue and pagenumbers.Link to publicationGeneral rightsCopyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright ownersand it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.            • Users may download and print one copy of any publication from the public portal for the purpose of private study or research.            • You may not further distribute the material or use it for any profit-making activity or commercial gain            • You may freely distribute the URL identifying the publication in the public portal.If the publication is distributed under the terms of Article 25fa of the Dutch Copyright Act, indicated by the “Taverne” license above, pleasefollow below link for the End User Agreement:www.tue.nl/taverneTake down policyIf you believe that this document breaches copyright please contact us at:openaccess@tue.nlproviding details and we will investigate your claim.Download date: 16. Nov. 2023/ department of mechanical engineering / Mechanics of MaterialsIntroductionStretchable electronics is a new field aiming to enablea range of bio-compatible futuristic devices (Fig. 1,2).Interface delamination is a precursor to the failure ofstretchable electronics made of elastically mismatchedmetal interconnects and rubber matrix materials.Figure 1: Intraocular retinalsensor arrayFigure 2: Neural activity monitor-ing arrayGoals1. Obtain insights in the macroscopic delaminationmechanics of copper-rubber interfaces.2. Develop a method to test and characterize theseinterfaces at microscopic scales.Macroscopic interface testingReal-time in-situ ESEM imaging of the progressing de-lamination front shows that (Fig. 3) interfaces that havethe highest work of separation (GC ) do not have thecleanest surface. Showing that, delamination is a deli-cate balance between the forming, elongation and rup-ture of fibrils and interface debonding.TPU, Ar = 5.9%, Gc = 3.7kJ/m2 PDMS, Ar = 87%, Gc = 1.3kJ/m2Figure 3: (top) ESEM images of the rubber area fraction Ar on thecopper after peeling, rubber is shown in black and copper in yellow.(bottom) Fibrilation of the progressing delamination front.Microscopic interface testingThe bulge test is used as a loading platform for thestretchable electronics, originally designed to charac-terize thin films, it is enhanced with global DIC to cap-ture local stress-strain information needed to measureinhomogeneous films.−100 −500 50100−500501020304050 g fx [µm]y [µm]z [µm]Figure 4: Two measured bulge test profiles f and g at 5% and10% strain respectively. A pattern is applied on the surfaceusing 80-500 nm Ag particles. In global DIC, the image g ismapped onto f by fitting its deformation u(x) by minimizing η2 =∫(f(x)− g {x + u(x)})2 dx.The quasi 3D data obtained from Confocal (or AtomicForce) Microscopy required a new DIC method becausethe pattern (Fig. 4), used to correlate with, also movesin the out of plane direction. The global DIC method isdeveloped in cooperation with F. Hild.x [µm]y [µm]Ux  −100 −50 0 50 100−50050z [µm]−2−1012x [µm]y [µm]Uy  −100 −50 0 50 100−50050z [nm]−20−1001020x [µm]y [µm]Uz  −100 −50 0 50 100−50050z [µm]−15−10−5Figure 5: The displacement fields in x, y and z obtained from theglobal DIC method, using basis functions of the type ϕn = xayb.Conclusions• Fibrilation of the rubber is observed, where50µm long fibrils are formed.• A delicate balance arises between the rupture ofthe fibrils and delamination of the interface.• The rubber fraction on the delaminated Cu sur-face decreases with increasing rubber toughnessand/or decreasing interface adhesion.• A 2D+ global DIC method is developed, usefulfor confocal, interferometry, and atomic force mi-croscopy data.• Which is very robust, even with 5% strain steps,yielding continuous full field displacement fields(Fig. 5), with sub pixel displacement resolution.A novel route towards interfaceintegrity in stretchable electronicsJ. Neggers, J.P.M. Hoefnagels and M.G.D. Geers

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A novel route towards interface integrity in stretchable electronics

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